Satellite positioning has numerous advantages. For example, the satellite positioning has a high global coverage rate (up to 98%), a high precision and a wide application scope, is quick and time-saving, and allows for mobile positioning. Therefore, the satellite positioning has become an important representative technology for outdoor positioning.
The positioning process of a conventional satellite positioning receiving device may be divided into three procedures, namely, an acquisition procedure, a tracking procedure and a positioning procedure. During the acquisition procedure, the satellite positioning receiving device calculates a code phase and a Doppler shift of a visible satellite in the sky. During the tracking procedure, the satellite positioning receiving device synchronizes a local signal to the satellite signal to analyze parameters such as the satellite ephemeris. The satellite ephemeris is a parameter indispensable for the subsequent positioning procedure, and comprises an absolute transmitting time of the satellite and the satellite orbit information. During the positioning procedure, the satellite positioning receiving device obtains the correct satellite position and the correct pseudorange between the satellite and the satellite positioning receiving device according to the parameters including the satellite ephemeris and calculates a position where it is located.
For the conventional satellite positioning receiving device, it will be impossible to obtain the absolute transmitting time of the satellite and the satellite orbit information once the conventional satellite positioning receiving device fails to obtain the satellite ephemeris during the tracking procedure. Absence of the absolute transmitting time of the satellite and the satellite orbit information will make it impossible for the conventional satellite positioning receiving device to obtain the correct satellite position and the correct pseudorange between the satellite and the satellite positioning receiving device, and as a result, the position of the user cannot be calculated.
The conventional satellite positioning receiving device may comprise a radio frequency (RF) front-end unit, a satellite signal acquisition unit, a satellite signal tracking unit and a position calculating unit. The RF front-end unit is used as a communication interface between the satellite and the satellite positioning receiving device, and the satellite signal acquisition unit, the satellite signal tracking unit and the position calculating unit are used to perform the acquisition procedure, the tracking procedure and the positioning procedure respectively. Because the satellite transmits the satellite ephemeris at a very low transmission rate (about 50 bps), it takes the satellite signal tracking unit much time (about 30 seconds to a few minutes) to download and process a whole piece of satellite ephemeris data (including the absolute transmitting time of the satellite and the satellite orbit information). Therefore, most of conventional satellite positioning receiving devices are confronted with an urgent problem to be tackled: that is, the speed of an initial positioning (or termed as “cold start”) is very low, so the user has to wait for a too long time, which may have an effect on the applications of the satellite positioning receiving devices.
Accordingly, an urgent need exists in the art to improve the problem that the conventional satellite positioning receiving devices have a very low initial positioning speed because the satellite signal tracking unit thereof must spend much time to download from the satellite and process a whole ephemeris of the satellite.